The conventional use of lengths of cable or wire cast into a concrete element, such as a concrete wall or a slab, to form a lifting hook for lifting of the element is unsafe and the hooks are prone to damage.
Modern lifting systems utilise lifting anchors which are partially cast and embedded in a concrete element that is to be lifted. The lifting anchors have a forged head which is exposed to engage with a hooking device mown as a ‘lifting eye’. Recesses are commonly provided on the surface of the concrete element at locations where there is a lifting anchor such that the exposed portion including the forged head of the individual lifting anchors is recessed below the concrete surface being protected from damages.
A recess is commonly formed and shaped by a recess former which is provided to encapsulate the exposed portion of the lifting anchor during curing of the concrete element. Known recess formers are in the shape of either a hemisphere or a truncated hemisphere with two planar sides. It is practically convenient and cheap to cast a hemispherical recess using a hemispherical recess former rather than formers having planar sides. Recess formers are often subject to problems of orientation and difficulties arise when disengaging the lifting eye. This is due to the fact that the lifting eye swivels about the head of the anchor but can only be disengaged once it is orientated. After a concrete wall has been leveraged up, it is simply too dangerous and impractical for a workman to climb up a ladder and manually release the lifting eye. It is therefore desirable that the lifting eye can be disconnected remotely.
Previous attempts to solve this problem have involved the use of truncated hemispherical formers with planar sides. These improved treated formers are advantageous in that the flat sides of a recess that is shaped by these formers restrict the rotational movement of the lifting eye. As a result, the lifting eye can be remotely released by pulling a cable or a wire which is connected thereto, since the rotational movement of the lifting eye is unidirectionally restricted. However, truncated hemispherical formers are often expensive to manufacture, and vulnerable to inaccuracies when orientated within a concrete element. The truncated formers are also often subject to movement during curing, the result of which requires the positioning of a supporting means, for example a chair, which carries each former, so as to consolidate the position of the former. Furthermore, given the nature of the common construction workplace, the supporting means having a former therein are often susceptible to inadvertent shifting or movement, for example, by workmen.